(1) Technical Field
The subject invention is directed toward a compressor having a control valve which controls the flow of discharge refrigerant generated by a small, continuously driven, auxiliary compressor as well as discharge refrigerant from the primary compressor itself to either act on a pressure responsive clutch which translates torque between input and output shafts thereby driving the primary compressor or to direct flow away from the pressure responsive clutch which terminates torque translation between the input and output shafts.
(2) Description of the Prior Art
Fluid pumping assemblies such as refrigerant compressors used for compressing a recirculating refrigerant in automotive air conditioning systems generally include some type of clutch mechanism to translate power from a power input source to the drive shaft of the compressor. One standard clutch mechanism commonly in use today includes a continuously driven pulley which is rotatably supported about a tubular extension of a clutch housing via ball bearings. The pulley is driven from the power take off of an automotive engine using a belt in the form of an endless loop as is commonly known in the art. An electromagnetic coil or solenoid generates an electromagnetic force which acts to draw an armature plate across a predetermined gap into frictional engagement with a rotating clutch friction plate. The armature plate is movably mounted to a hub using springs or an elastomeric support member. The hub, in turn, is fastened to a compressor drive shaft. When the coil is energized, the clutch friction plate imparts rotation to the armature plate which, in turn, causes the hub and the compressor drive shaft to rotate thereby driving the compressor.
Examples of electromagnetically actuated clutches employed with refrigerant compressors can be found at U.S. Pat. No. 4,296,851, issued to Pierce on Oct. 27, 1981; U.S. Pat. No. 4,616,742 issued to Matsushita on Oct. 14, 1986 and the clutches disclosed in U.S. Pat. No. 5,195,625, issued to Change et al. on Mar. 23, 1993, and U.S. Pat. No. 5,180,291, issued to Kent on Jan. 19, 1993, both of which are assigned to the assignee of the subject invention.
Although clutches of the type disclosed in the aforementioned patents and described above have long been employed in compressors used in automotive applications, they are not without their problems. One of the most common sources of warranty problems for air conditioning compressors comes from the failure of the solenoid or coil. The clutch coils are expensive and difficult to replace and typically when they fail, the entire compressor is scrapped.
In addition, the externally mounted, dry, electromagnetic clutches are not tolerant of slow engagement which is a desirable characteristic to the consumer. Such clutches wear excessively if engaged slowly. The provision of slow engagement also increases the cost of the electrical control means.
Other clutch mechanisms have been disclosed which employ the compressor discharge pressure to cause frictional engagement between adjacent clutch plates thereby translating torque between input and output shafts. One such example of this type of clutch mechanism can be found in U.S. Pat. No. 4,715,800 issued to Nishizawa et al on Dec. 29, 1987 and its divisional U.S. Pat. No. 4,828,463 issued on May 9, 1989. The disclosure of both of the Nishizawa patents are identical and therefore will be discussed collectively.
The Nishizawa '800 and '463 patents are directed toward a rotary compressor with a clutch and bypass control actuated by hydraulic and/or compressed fluid. More specifically, these patents disclose a compressor having an electromagnetically actuated valve which controls the flow from a continuously driven small trochoid pump which generates a hydraulic discharge pressure which acts on a pressure responsive clutch plate to cause an initial drive of the compressor. The compressor discharge pressure is then employed to act on the pressure responsive clutch plate to cause full clutch engagement to drive the compressor.
Although the Nishizawa '800 and '463 compressors do not disclose the use of a clutch which employs a solenoid or clutch coil, the control valve disclosed by Nishizawa is complex and must accommodate both refrigerant and hydraulic fluid. Furthermore, the porting necessary to cause clutch actuation using a hydraulic fluid as well as a refrigerant discharge pressure in the Nishizawa compressor is rather complex and increases the cost of such compressors.